1. Field of the Invention
This invention relates to electronic monitoring and control circuits. More particularly, this invention relates to electronic drive circuits used to monitor and control direct current (DC) motors.
2. Description of Related Art:
DC motors are used in many applications to move machines or position parts of machines with respect to each other. Many of the existing applications use electronic drive circuits to control the DC motor. A problem in any such circuit is determining when the machine or part being moved has reached the end of its travel, so that the electric current driving the DC motor can be eliminated or reversed to stop the motor or reverse its direction, thereby preventing damage to the DC motor or machine.
All such control circuits in the past have relied on mechanical sensors external to the control circuit to sense when the moving machine or part has reached the end of its travel, and to cut off or reverse the electrical current to the DC motor. For example, a switch would be mounted at the end of a rail along which the machine or part is moved. When the machine or part contacts the switch, the switch either creates an open circuit which eliminates the current and stops the motor, or the switch reverses the polarity of the current and reverses the motor direction. Optical sensors, wherein the moving part breaks a beam of light, have also been used to perform the function of the switch.
The use of external mechanical sensors, however, adds greater complexity and cost to DC-motor control systems. This complexity results in higher cost of production, reduced reliability, and therefore, higher maintenance costs over the life of the systems.